The present invention relates to waveform digitizing systems, and more particularly to a multi-channel trigger dejitter technique for digital sampling oscilloscopes and the like that improves the accuracy of the trigger time information for repetitive signals.
A waveform digitizing system, such as a digital sampling oscilloscope, takes discrete periodic samples of multiple analog input signals and either displays them or otherwise stores or transmits them to a remote device, such as a personal computer. If a signal is repetitive and being displayed, it is important that each iteration of the signal be displayed in the same place so that parts of the waveform that are not different do not move around and differences between subsequent iterations are readily apparent. The trigger hardware of a digital sampling device ensures that signals are always digitized in the vicinity of a particular event, such as a voltage crossing. Trigger time information is typically provided to much higher resolution than the digitizing sample interval. For example, a digital sampling oscilloscope with a digitizing sample interval of 500 picoseconds might provide trigger time resolution of ten picoseconds. This allows the display to be horizontally expanded, i.e., "zoomed", either using software interpolation, such as linear or sin(x)/x algorithms, or using equivalent time sampling where the display is filled out over multiple acquisitions. If high resolution trigger time information is not provided accurately, an interpolated display jitters back and forth and an equivalent time sampling display shows vertical noise on edges because of errors in sample time placement with respect to the trigger point.
Therefore what is desired is a multi-channel trigger dejitter technique for digitizing sampling devices that uses information contained in the digitized waveform to improve the accuracy of the trigger time information for repetitive signals.